(1) Field of the Invention
The present invention relates to an electromagnetic anechoic chamber which provides a closed space for containing an electromagnetic device radiating an electromagnetic wave and for suppressing echo of the radiated electromagnetic wave in the space.
(2) Description of the Prior Art
Presently, various electric and electronic devices, and apparatus including radio systems are in use. Radio systems use and emit electromagnetic waves in space as information transmission media. It is known that electric and electronic devices other than radio systems radiate unintended electromagnetic waves.
Therefore, those electric and electronic devices are collectively called electromagnetic devices.
It is also known that when an electromagnetic device radiates, as a source, such an unintended electromagnetic wave, the unintended electromagnetic wave often obstructs, as noise, the operation of other electromagnetic devices disposed near the source. Therefore, it is desired for all of the electromagnetic devices that such an unintended radiation is as low in level as possible.
In order to counteract the unintended radiation of an electromagnetic device, it is necessary to know the actual and precise level of the unintended radiation itself. It is necessary that measurement of the unintended radiation of the electromagnetic device is carried out under the condition that no electromagnetic wave exists other than the unintended radiation.
Further, it is always required for radio systems to measure their radiation and reception properties of intended electromagnetic waves. Such a measurement also requires a similar condition where no radiation exists other than the intended electromagnetic wave.
In order to provide such a condition for measurement of electromagnetic radiation from an electromagnetic device, an electromagnetic anechoic chamber is known in the prior art.
A conventional electromagnetic anechoic chamber comprises a shielding wall of metal which has an inner surface and an electromagnetic wave absorber layer secured on and covering the inner surface of the shielding wall. Thus, the electromagnetic wave absorber layer defines a closed space. An electromagnetic device to be tested is disposed in the closed space.
The shielding wall prevents any external electromagnetic waves from entering the closed space. The electromagnetic wave absorber layer does not reflect but absorbs the electromagnetic wave emitted from the electromagnetic device disposed in the closed space. As a result, entering neither entering external electromagnetic wave nor echo of the electromagnetic wave emitted from the electromagnetic device in the closed space are present in the closed spaced. Therefore, it is possible to directly measure the electromagnetic wave emitted from the device into the closed space.
However, the conventional electromagnetic anechoic chamber is disadvantageous in that the chamber is expensive because the electromagnetic wave absorber layer must be secured over the entire area of the inner surface of the shielding wall.